Laser capillary support spacer

ABSTRACT

A laser is described in which a diaphragm of flexible electrically non-conductive material is used to at least partially support an elongated capillary within a tubular glass envelope. The diaphragm separates the glass envelope into positive and negative discharge chambers and is in the shape of an annular channel member with inner and outer annular walls. Such walls engage the capillary and the inner surface of the envelope, respectively, along a length sufficient to prevent discharge between the positive and negative discharge chambers.

Umted States Patent 3,683 300 9 Hohenstein Aug. 8, 1972 [54] LASERCAPILLARY SUPPORT SPACER Primary Examiner-William L. Sikes AssistantExaminerR. J. Webster 72 I t k H. H h t 1234 L l 1 nven or {li z gfi94549 aure Attorney-Fitch, Even, Tabin and Luedeka [22] Filed: Aug. 19,1970 [57] ABSTRACT [21] Appl. No.: 65,018 A laser is described in whicha diaphragm of flexible I electrically non-conductive material is usedto at least 52] U 8 Cl 331/94 5 313/204 partially support an elongatedcapillary within a tubu- 1 3018 1/06 lar glass envelope. The diaphragmseparates the glass envelope into positive and negative discharge cham-[58] Field of Search ..33l/94.5, 313/204 bars and is in the shape of anannular channel member [56] Reterences Cited with inner and outerannular walls. Such walls engage UNITED STATES PATENTS the capillary andthe inner surface of the envelope, respectively, along a lengthsufficient to prevent discharge between the positive and negativedischarge Arnold et al ..313/204 chambers. 3,528,028 9/1970 Baird..331/94.5 3,566,302 2/1971 Rhodes ..331/94.5 9 Chums, 6 Drawing FiguresFOREIGN PATENTS 0R APPLICATIONS 6,707,770 l2/l967 Netherlands...331/94.s

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- 1 '5I\M it 50 2/53 E IE g 39M 41M 33 in 1 LASER CAPILLARY SUPPORTSPACER This invention relates generally to lasers and, moreparticularly, to an improved laser of economical construction.

The laser is acquiring greater importance as a useful tool in a varietyof applications. Lasers are used in many forms for instrumentation,communication, and even for various types of surgery. Laser light isuseful in such applications because it is monochromatic, coherent (allradiation is in phase), highly dense, and high in frequency.

The helium-neon coaxial gas laser is a particularly useful type of laserbecause of its relative simplicity and because of the convenientwavelength (6,328 Angstrom units) in the visible red region of thespectrum. In a helium-neon gas laser, helium gas is excited by a d-c orRF discharge in a non-conducting container. One of the helium energylevel transitions caused by the discharge excites the neon atoms to aparticular energy level. One of the neon energy level decay transitionsreleases radiation at the 6328 Angstrom units wavelength.

In a helium-neon coaxial gas laser, in order to constrain the excitedatoms and make them available for stimulation, a capillary is used. Thiscapillary typically consists of a glass tube suspended coaxially insidethe envelope of the laser. In order to concentrate the early radiationproduced by the laser, which is typically randomly directed, and thusstimulate other excited atoms to produce a large quantity of visiblelight, mirrors are typically used at the ends of the glass envelope oroutside the glass envelope. These mirrors reflect light energy back intothe envelope to hit more excited neon atoms and thus contribute to arapid multiplication of stimulated radiation. One of the reflectivemirrors should be slightly less reflective than the other and, when thelight bouncing back and forth between the two mirrors is sufficientlyintense, a beam of light will pass through the weaker mirror. It is thisbeam of light, which is coherent, monochromatic, and of very highdensity and frequency, which is useful in the many applications oflasers.

A significant deterrent to the widespread use of lasers has been therelatively high cost of manufacturing such devices. The two factorswhich contribute most substantially to the cost of manufacturing acoaxial gas laser are the mirrors used to reflect the light and theglass blowing which is typically necessary in manufacturing the envelopeand the capillary therein. In manufacturing a coaxial laser wherein thecapillary is suspended inside the envelope, a series of operations arenecessary that result in the internal suspension of the capillary whilesimultaneously separating or dividing the envelope into positive andnegative discharge chambers. By separating the positive and negativedischarge chambers, the high potential therebetween is forced to passthrough the capillary. This action increases the density of excitedatoms and therefore increases the lasers gain. Since glass is the onlymaterial that is practical for a laser of this type, partially becauseit can be formed and partially because it does not conduct electricity,the manufacture of a laser of this type has typically necessitated thatthe outer glass envelope be cut apart, joined to the capillary, and thenreunited with its separated half. This operation does not lead itself toautomation but rather has heretofore required relatively expensive handglass blowing.

Accordingly, it is an object of the present invention to provide animproved laser.

Another object of the present invention is to provide a coaxial laser ofthe helium-neon type in which the amount of hand glass blowing that isrequired is substantially reduced.

Another object of the invention is to provide an improved laser which iscapable of being assembled automatically or by a semi-skilled worker.

It is another object of the invention to provide a coaxial laser whereinthe strength of the envelope is substantially increased and wherein thedimensions are more closely regulated than in prior art designs.

Other objects of the invention will become apparent to those skilled inthe art from the following description taken in connection with theaccompanying drawings wherein:

FIG. 1 is a full section view of a laser constructed in accordance withthe invention;

FIG. 2 is an end view of a diaphragm used in the laser of FIG. I viewedfrom the left-hand side thereof as seen in FIG. 1;

FIG. 3 is a view of the diaphragm of FIG. 2 from the opposite sidethereof; and

FIGS. 4, 5, and 6 are plan views of three types of springs which areutilized in the laser of FIG. 1.

Very generally, the laser of the invention comprises a tubular glassenvelope 1 1. An elongated capillary 13 is disposed axially within theenvelope. A diaphragm 15 of flexible electrically non-conductivematerial at least partially supports the capillary within the envelope.The diaphragm divides the interior of the envelope into positive andnegative discharge chambers 17 and 19. The diaphragm comprises anannular channel member having an outer annular wall 21 and an innerannular wall 23 separated by at least one annular channel 25. The innerannular wall engages the capillary and the outer annular wall engagesthe inner surface of the envelope along a length in each case sufiicientto prevent discharge between the chambers 17 and 19 except through thecapillary.

Referring now more particularly to FIG. 1, the glass envelope 11 is inthe form of an elongated tube and has its ends closed by a pair ofmirrors 27 and 29. The mirrors are joined about their periphery to theends of the glass tube by means'of an epoxy or other suitable sealant.One of the mirrors 27 and 29 is capable of passing some lighttherethrough in order to allow the laser to emit the coherentmonochromatic 'light produced therein. Alternatively, the ends of thetube may be closed by transparent glass discs and mirrors may bepositioned externally of the envelope in axial alignment therewith forreflecting light back into the capillary 13. In such a case, the ends ofthe tube need not be cut square as shown, but rather may be cut to liein a plane which is at an oblique angle with the axis of the tube ratherthan perpendicular thereto. The angle selected may be the so-calledBrewsters angle, which enables enhancement of a particular wavelengthfor production by the laser.

The capillary 13 is supported, by means subsequently described, thetubular envelope 11 in coaxial relation thereto. The capillary 13 has anaxial capillary passage 30 therein in which the laser action takesplace, as is known in the art. The passage 30 provides communicationbetween the positive and negative discharge chambers 17 and 19, andenables a flow of electrons therebetween.

In order to produce a flow of electrons through the capillary 13, theenvelope 11 contains a pair of electrodes 31 and 33 at the respectiveends thereof. These may be bare wires, or they may be cylinders asshown. The bare wires should be tungsten or other material resistive tobombardment by ions. The cylinders are of a cold cathode design familiarto those knowledgeable in the art. The diameter of the cylinders andtheir length depends on the surface area desired, but the inner diameterof the cylinders should exceed the diameter of the passage 30 in thecapillary 13. Electrical connection from outside of the envelope is madeto the cylinder 31 by a thin strip of metallic foil or conductive paint35 passed through the joint between the mirror 27 and the end of thetube. A similar thin foil or conductive paint strip 37 provides externalconnection to the metallic cylinder 33. The cylinders 31 and 33 serve asthe anode and cathode of the laser by connection across a suitablesource of potential, not shown. The particular configuration of anodeand cathode shown provides a very efficient discharge and collection ofelectrons in the laser. The regions where the strips of foil orconductive paint 35 and 37 pass out of the en velope may be sealed withepoxy to ensure the integrity of the tube.

In order to evacuate the interior of the envelope 11 and to fill therespective chambers 17 and 19 with the appropriate gas, the envelope isprovided with a pair of evacuation ports 39 and 41, positioned towardsrespective ends of the envelope. As will be explained subsequently indescribing the assembly of the laser of the invention, the evacuationports 39 and 41 are sealed by appropriate means, such as tipping offwith a torch as is known in the art, once the respective chambers 17 and19 are filled with the appropriate type of gas. A single evacuation portcould be used, rather than the two shown, but the narrow passage 30would make such a procedure inefficient.

In order to electrically. separate the discharge chambers l7 and 19 toforce the electrons through the passage 30 in the capillary 13, manyprior art devices have utilized a glass wall formed integral with orsealed to the envelope and the capillary. As previously mentioned, thissubstantially increases the cost of manufacturing the laser. Inaccordance with the invention, the diaphragm 15 is utilized for thispurpose.

Referring to FIGS. 2 and 3 in addition to FIG. 1, the particularconfiguration of the diaphragm 15 is of generally U-shaped cross sectionand defines an outer annular wall 21 and an inner annular wall 23 joinedby a web 43 which constitutes the bottom of the U. Another way ofdescribing the diaphragm is that it is in the form of an annular channelmember which defines an annular open-sided channel 25 separated by theannular walls 21 and 23. The outer annular wall 21 is generally coaxialwith the tubular envelope l1 and engages the inner surface thereof alonga substantial axial distance. Similarly, the inner annular wall 23 isgenerally coaxial with the capillary 13 and extends a substantialdistance along the outer surface thereof in engagement therewith.

Although the U-shaped cross section of the annular channel membercomprising the diaphragm 15 is the preferred configuration, theinvention is not limited thereto. Thus, the diaphragm may comprise anannular channel member of any convenient cross section, provided thatthe outer and inner walls can resiliently engage the envelope andcapillary, respectively, (to facilitate assembly), and provided that thedistance of engagement is sufiicient to prevent discharge as describedbelow. One example of an alternative form is an annular channel memberhaving a cross section in the shape of the cross section of an I-beam.In such a case, both edges of the annular inner and outer walls would becapable of flexing. If the walls are made slightly convex with respectto the surfaces they engage, a region of contact can be provided.

A discharge path between the discharge chambers 17 and 19 which is oflower resistance than the path through the passage 30 in the capillary13 will deleteriously affect the performance of the laser. For example,where the discharge voltage through the capillary is 5,000 volts, avoltage path outside of the capillary of, for example, 2,000 volts willresult in a discharge directly between the two chambers and not throughthe capillary. Such a situation is prevented by the diaphragm of theinvention by providing a substantial distance of contact between thediaphragm and the glass surfaces which it engages, thereby presenting apotential breakdown path between the chambers which is of higherresistance than the path through the capillary 13.

In order to provide this, the diaphragm is made of a flexibleelectrically non-conductive material. The material should havesufficient flexibility as to maintain the necessary contacting pressureagainst the glass surfaces as to prevent discharge therealong and, inaddition, to provide at least partial support for the capillary 13. Theouter diameter of the diaphragm increases toward the open side of thechannel 25, and the inner diameter of the diaphragm decreases toward theopen side of the channel 25. In some cases, the resilience of thematerial may be insufficient. To this end, in the illustratedembodiment, the channel side of the outer annular wall is provided withan annular groove 45 and the channel side of the inner wall is providedwith an annular groove 47. A spring 49 is provided in the groove 45 tobias the outer wall outwardly against the inner surface of the envelope1 1. Similarly, a spring 51 is provided in the groove 47 to bias theinner wall of the diaphragm inwardly against the outer surface of thecapillary 13.

The spring 49 is illustrated in FIG. 4 and the spring 51 is illustratedin FIG. 5. The spring 49 is a loop with overlapped ends which can becompressed during assembly and which expands into the groove 45. Thespring 51 is an unclosed loop which may be expanded by separating itsends for assembly, and which compresses itself into the groove 47.

The flexibility of the diaphragm 15 is also of advantage in order tocompensate for the fact that glass tubes, as supplied by commercialmanufacturers, are typically never exactly one dimension. For example,variations in diameter may exceed 0.05 inch in a glass tube of a nominalinside diameter of 0.8 10.

The material of which the diaphragm 15 is made is also of a materialwhich has a very low outgassing rate under the conditions of laseroperation. This is in order to prevent contamination of the tube as aresult of partial vaporization of the diaphragm material. A material ispreferred having an outgassing or desorption rate of less than about 5 XTorr liters per second per square centimeter after 48 hours under vacuumat room temperature. By vacuum, a pressure of less than 20 Torr ismeant. A satisfactory flexible insulating material for this purpose ispolytetrafluorethylene, sold under the trademark TEFLON. Anothersatisfactory material is that sold under the trademark VTTON sold by theEdwards Company.

The axial distance of contact between the diaphragm and the envelope 1 land the capillary l3 depends on the angle of the non-engaging portionsof the surfaces, the pressure of the gas in the envelope, and thevoltage drop between the chambers 17 and 19. The greater the anglebetween the non-engaging portions of the adjacent surfaces (i.e., theouter wall 21 and the envelope 11 or the inner wall 23 and the capillary13), the less the resistance offered by the gap therebetween and hencethe greater the required contact distance to prevent breakdown. Agreater contact distance is also needed with higher gas pressure, sincethe gas is more easily ionized. Finally, of course, a higher potentialdifference requires a greater contact distance. The total axial lengthof the diaphragm is preferably about one and one quarter time the innerdiameter of the envelope.

In some cases, particularly where the capillary is of substantiallength, the diaphragm 15 may be insufficient to provide the propersupport for the capillary. In such a case, the spring support 53 isprovided, the latter being illustrated more fully in FIG. 6. The outerpart of the spring support 53 bears against the inner surface of theenvelope 1 1 and the inner part is formed with a pair of detents 55 forcapturing the capillary 13.

In assembling the illustrated laser, the diaphragm 15 is first placed onthe capillary 13 and the inner spring 51 is put in place in the groove47. The assembly is then inserted into the open-ended envelope 11 to theproper location and the outer spring 49 is put in place in the groove45. The support spring 53 is then put in place as are the electrodes 31and 33 and their foil strip connections 35 and 37. The mirrors 27 and 29are then cemented on with an epoxy. The tube is then evacuated by meansof a suitable pumping system, preferably with a 0.001 milligrams persecond or less contamination rate. The tube chambers 17 and 19 are thenfilled with helium and neon to the proper pressure, depending upon theoptical geometry and resonator design, as is known in the art. Althoughnot absolutely necessary, a getter is preferably included. A getter is achemically active material that captures contaminants and prevents thecontaminants from poisoning the gas in the tube. This getter can beintroduced to the inside of the tube by means of a movable anode, noshown, through the evacuation ports. Once the tube is filled withappropriate gases at the appropriate pressure, the evacuation ports 39and 41 are then suitably sealed.

It is also preferable that the cathode and perhaps the anode be preparedby one or several of the following steps:

a. Heating in vacuum by RF induction heating;

b. Heating in helium, helium-neon, neon or oxygen by RF inductionheating;

c. Heating in helium, helium-neon, neon or oxygen by DC discharge; and

d. Heating in helium, helium-neon, neon oxygen or vacuum by means of anexternal heater. Item c. above requires either an additional electrodein the tube or a movable electrode situated in the evacuation port. Themovable electrode may be advanced for operation and retracted when thetube is sealed off.

In the case of the mirrors 27 and 29 it is necessary that the mirrors beproperly aligned, as is known in the art, when mounted on the envelope.If external mirrors are used, alignment of the blanks or transparentends 27 and 29 is according to the chosen angle.

It may therefore be seen that the invention provides an improved laserof the coaxial type in which the amount of glass blowing required issignificantly reduced. Moreover, the laser is readily assembled in amanner such that a semiskilled worker or even an automated system may beutilized. No complex glass joints are required and the envelope istherefore stronger. For the same reason, minimal internal stressesresult from the disclosed construction. Finally, the various dimensionsof the portions of the laser are easily regulated.

Various modifications of the invention in addition to those shown anddescribed herein will become apparent to those skilled in the art fromthe foregoing description and accompanying drawings. Such modificationsare intended to to fall within the scope of the appended claims.

What is claimed is:

l. A laser comprising, a glass envelope, an elongated capillary disposedaxially within said envelope, and a diaphragm of flexible electricallynon-conductive material at least partially supporting said capillary anddividing the interior of said glass envelope into positive and negativedischarge chambers, said diaphragm comprising an annular channel memberhaving outer and inner annular walls separated by at least one flexibleannular transverse wall to define at least one annular channel, saidinner annular wall engaging said capillary and said outer annular wallengaging the inner surface of said envelope along a length of saidcapillary and said envelope sufficient to prevent discharge between saidpositive and negative discharge chambers other than through saidcapillary.

2. A laser according to claim 1 wherein said diaphragm is comprised of amaterial having an outgassing rate of less than about 5 X 10" Torrliters per second per square centimeter after 48 hours under vacuum atroom temperature.

3. A laser according to claim 1 including means for resiliently biasingsaid outer annular wall of said diaphragm outwardly against saidenvelope, and including means for resiliently biasing said inner annularwall of said diaphragm inwardly against said capillary.

4. A laser according to claim 1 wherein said channel member is ofgenerally U-shaped cross section defining a single channel having anopen side.

5. A laser according to claim 4 wherein said diaphragm is provided withannular grooves on the channel side of said inner and outer wallsadjacent the open side of said channel, and a pair of annular springsmating in said grooves, respectively, to bias said outer annular wallagainst said envelope and said inner annular wall against saidcapillary.

6. A laser according to claim 1 including means displaced along saidcapillary from said diaphragm for providing additional support for saidcapillary within said envelope.

7. A laser comprising an elongated tubular glass envelope having a pairof evacuation ports spaced axially therealong, a pair of electrodesspaced axially within said envelope, an elongated glass capillarydisposed within said envelope lying along the axis of said tubularenvelope, a diaphragm of flexible electrically nonconductive materialpartially supporting said capillary and positioned between said pair ofevacuation ports and between said pair of electrodes, dividing theinterior of said glass envelope into positive and negative dischargechambers, said diaphragm comprising an annulus of generally U-shapedcross section to define outer and inner annular walls separated by anannular channel, said inner annular wall engaging said capillary andsaid outer annular wall engaging the inner surface of said envelopealong a length of said capillary and said envelope sufficient to preventdischarge between said chambers other than through said capillary, and asupport member positioned along said capillary displaced 8 from saiddiaphragm for partially supporting said capillary.

8. For use in a laser having a capillary coaxially positioned within atubular envelope, a diaphragm for maintaining separation betweenpositive and negative discharge chambers in the envelope, said diaphragmbeing comprised of flexible electrically non-conductive material formedin an annulus of generally U-shaped cross section to define inner andouter annular walls separated by an annular channel, at least part ofsaid inner annular wall being of a diameter to engage the capillary andat least part of said outer annular wall being of a diameter to engagethe envelope, said parts of said outer and inner annular walls being ofan axial length sufficient to prevent discharge between the positive andnegative discharge chambers of the laser other than through thecapillary.

9. A diaphragm according to claim 8 wherein said outer annular wall isof increasing diameter toward the open side of said annular channel, andwherein said inner annular wall is of decreasing diameter toward theopen side of said annular channel.

1. A laser comprising, a glass envelope, an elongated capillary disposedaxially within said envelope, and a diaphragm of flexible electricallynon-conductive material at least partially supporting said capillary anddividing the interior of said glass envelope into positive and negativedischarge chambers, said diaphragm comprising an annular channel memberhaving outer and inner annular walls separated by at least one flexibleannular Transverse wall to define at least one annular channel, saidinner annular wall engaging said capillary and said outer annular wallengaging the inner surface of said envelope along a length of saidcapillary and said envelope sufficient to prevent discharge between saidpositive and negative discharge chambers other than through saidcapillary.
 2. A laser according to claim 1 wherein said diaphragm iscomprised of a material having an outgassing rate of less than about 5 X10 8 Torr liters per second per square centimeter after 48 hours undervacuum at room temperature.
 3. A laser according to claim 1 includingmeans for resiliently biasing said outer annular wall of said diaphragmoutwardly against said envelope, and including means for resilientlybiasing said inner annular wall of said diaphragm inwardly against saidcapillary.
 4. A laser according to claim 1 wherein said channel memberis of generally U-shaped cross section defining a single channel havingan open side.
 5. A laser according to claim 4 wherein said diaphragm isprovided with annular grooves on the channel side of said inner andouter walls adjacent the open side of said channel, and a pair ofannular springs mating in said grooves, respectively, to bias said outerannular wall against said envelope and said inner annular wall againstsaid capillary.
 6. A laser according to claim 1 including meansdisplaced along said capillary from said diaphragm for providingadditional support for said capillary within said envelope.
 7. A lasercomprising an elongated tubular glass envelope having a pair ofevacuation ports spaced axially therealong, a pair of electrodes spacedaxially within said envelope, an elongated glass capillary disposedwithin said envelope lying along the axis of said tubular envelope, adiaphragm of flexible electrically non-conductive material partiallysupporting said capillary and positioned between said pair of evacuationports and between said pair of electrodes, dividing the interior of saidglass envelope into positive and negative discharge chambers, saiddiaphragm comprising an annulus of generally U-shaped cross section todefine outer and inner annular walls separated by an annular channel,said inner annular wall engaging said capillary and said outer annularwall engaging the inner surface of said envelope along a length of saidcapillary and said envelope sufficient to prevent discharge between saidchambers other than through said capillary, and a support memberpositioned along said capillary displaced from said diaphragm forpartially supporting said capillary.
 8. For use in a laser having acapillary coaxially positioned within a tubular envelope, a diaphragmfor maintaining separation between positive and negative dischargechambers in the envelope, said diaphragm being comprised of flexibleelectrically non-conductive material formed in an annulus of generallyU-shaped cross section to define inner and outer annular walls separatedby an annular channel, at least part of said inner annular wall being ofa diameter to engage the capillary and at least part of said outerannular wall being of a diameter to engage the envelope, said parts ofsaid outer and inner annular walls being of an axial length sufficientto prevent discharge between the positive and negative dischargechambers of the laser other than through the capillary.
 9. A diaphragmaccording to claim 8 wherein said outer annular wall is of increasingdiameter toward the open side of said annular channel, and wherein saidinner annular wall is of decreasing diameter toward the open side ofsaid annular channel.